Conventionally, in the air-conditioning apparatus such as a multi-air-conditioning apparatus for building use, cooling operation or heating operation is carried out by circulating a refrigerant, for example, between an outdoor unit which is a heat source unit disposed outdoors and an indoor unit disposed indoors. Specifically, cooling or heating of the air-conditioning target space was performed with air heated by heat-transferring of refrigerant or air by heat-receiving of refrigerant. As a refrigerant used for such an air-conditioning apparatus, for example, HFC (hydrofluorocarbon) based refrigerants are often used, and natural refrigerants such as carbon dioxide (CO2) have been also suggested.
In the meantime, there is an air-conditioning apparatus of another construction represented by chiller system. In such an air-conditioning apparatus, cooling energy or heating energy generated in the heat source unit disposed outdoors cools or heats the heat medium (secondary refrigerant) such as water or nonfreezing fluid at a heat exchanger disposed in an outdoor unit and this heat medium is transported to a fan-coil unit or a panel heater or the like which is an indoor unit disposed in the air-conditioning target region to perform cooling or heating (for example, see Patent Literature 1).
There are air-conditioning apparatuses which are configured so that heat exchangers for the primary refrigerant and the secondary refrigerant may be disposed in the vicinity of the respective indoor units and the secondary refrigerant may be transported to the indoor unit (for example, see Patent Literature 3).
In addition, there are also air-conditioning apparatuses which are configured so that divergence units having an outdoor unit and a heat exchanger may be connected with two pipelines to transport the secondary refrigerant to the indoor unit (for example, see Patent Literature 4).